The present invention relates to an ink jet printer head using a piezoelectric device to jet ink, and an ink jet printer.
Ink jet printers are printers of the type that liquid ink is jetted into air in droplets, a liquid column or a spray to print letters, graphs, pictures, etc. on recording papers. It has motivated practice of the ink jet printers that the ink jet printers can have noises reduced, be smaller-size and lightened.
Heads for use in the ink jet printers are mainly of bubble type which generates air bubbles generated by a heater in a pressure chamber to jet ink from a nozzle by a force of the air bubbles, and piezoelectric type which has an oscillation plate on the bottom of a pressure chamber to press the oscillation plate by a piezoelectric material to jet ink from a nozzle.
The bubble type of these two types has limits to printing speed and print quality because performance of the head is determined substantially by characteristics of ink, which makes it difficult to meet higher speed and higher print quality. On the other hand, the piezoelectric type is expected to have higher performance than the bubble type because the piezoelectric type can easily meet higher speed, control ability and ink characteristics but has disadvantages of the complicated structure and being expensive.
As an ink jet printer head which solves these disadvantages of the piezoelectric type the applicant proposes in Japanese Patent Laid-Open Publication No. 192513/1996 a piezoelectric type ink jet printer head comprising a channel plate 110 for defining a plurality of discrete ink channels 112 and a piezoelectric device 100 which is parts of the walls of the discrete ink channels 112, which are connected with each other (see FIG. 8). Because this structure is very simple and has a small number of parts, this type could be inexpensive comparably with the bubble type. However, drive portions 106 of the piezoelectric device 100 opposed to the discrete ink channels 112 are restricted by the side surfaces and the bottom surfaces, whereby the drive portions 106 have poor displacing efficiency. In addition, each drive portions 106 is affected by the other drive portions 106, whereby a stroke of a displacement amount is large. The characteristics of the ink jet printer head are not satisfactory for an ink jet printer head.
Japanese Patent Publication No. 33087/1995 discloses an ink jet printer head having respective drive portions 140 divided by grooves 138 to thereby improve displacement efficiency (see FIG. 9). In this ink jet printer head, drive portions 140 of a piezoelectric device 130 corresponding to discrete ink channels 152 are separated by the grooves 138 and accordingly are not little restricted in displacement, so that large displacement amounts can be obtained in comparison with those of the conventional head shown in FIG. 8. However, on other hand, the bottoms of the drive portions 140 are connected to the base of the piezoelectric device 130, and disadvantageously displacements of the drive portions 140 are conducted to the other drive portions 140.
That is, when a voltage is applied to the drive portions 140, the drive portions 140 are extended upward by the vertical piezoelectric effect while being diminished widthwise by the lateral piezoelectric effect. Displacements of the drive portions 140 by the lateral piezoelectric effect, the bottoms of which are not separated from the base of the piezoelectric device 130 therebelow, cause the base contacting the drive portions 140 to diminish. Accordingly, a tensile stress is exerted to the rest part of the base and restricts displacements of the other drive portions 140. Thus, as a number of drive pins is larger, the drive pins restrict displacements each other to thereby vertical displacement amounts for pressing the respective ink channels 152 are decreased. In addition, displacements by the lateral piezoelectric effect become a huge stress at the forward ends of the grooves 138 due to stress concentration, which results in breaking devices and in decreasing reliability.
Furthermore in the head shown in FIG. 9, the piezoelectric layers 136 of the drive portions 140 are sandwiched by the drive electrodes 134. Generally adhesion strength between piezoelectric materials and electrode materials is low, and the electrode material and the piezoelectric material tend to peel off each other in their interface when the grooves 138 are processed. The same peeling tends to occur while being driven or after driven due to stresses generated when driven. Reliability is poor.
Additionally in the head shown in FIG. 9, the drive electrodes 134 and the piezoelectric layers 136 are formed not considering the drive portions 140 and the non-drive portions 142, and are divided by processing the grooves 138, and accordingly the drive electrodes 134 are also formed in the non-drive portions 140. A tensile stress is applied to the non-drive portions 142 when a voltage is applied to the drive portions 140 to press the ink channels, and the peeling tens to take place in the electrodes-ceramics interfaces whose strength is low.
For higher nozzle density it is necessary that the non-drive portions 142 have a width as small as possible, and the presence of the drive electrodes 134 in the non-drive portions 142 is a problem in view of reliability in processing the grooves 138 and driving.
As described above, the conventional ink jet printer heads are not satisfactory to meet both requirements of reduction of crosstalk and higher reliability.
An object of the present invention is to provide a ink jet printer head having little crosstalk, high reliability and high performance, and an ink jet printer of high performance using the ink jet printer head.
The above-described object is achieved by an ink jet printer head comprising: a piezoelectric device including: a stress removing electrode formed on a substrate; a stress removing piezoelectric layer formed on the stress removing electrode; and a drive layer having a pair of drive electrodes and a piezoelectric layer disposed between the pair of drive electrodes, the drive layer being divided in a plurality of drive portions and a plurality of non-drive portions by grooves which reach the stress removing piezoelectric layer; and a channel plate jointed to the piezoelectric device on a side where the drive layer is formed, and having a plurality of discrete ink channels formed in parts thereof respectively opposed to said plural drive portions, corresponding to nozzles for jetting ink.
In the above-described ink jet printer head, it is possible that the drive electrode and/or the stress removing electrode has all region thereof or a part of the region formed in a mesh.
In the above-described ink jet printer head, it is possible that a prescribed voltage is applied between the lowermost drive electrode and the stress removing electrode when the drive portions are driven to thereby mitigate a stress exerted to the stress removing piezoelectric layer.
In the above-described ink jet printer head, it is possible that a voltage to be applied to the drive electrode and a voltage to be applied to the stress removing electrode have equipotential.
The above-described object is also achieved by an ink jet printer head comprising: a piezoelectric device formed on a substrate, and including a drive layer having a pair of drive electrodes and a piezoelectric layer disposed between the pair of drive electrodes, the drive layer being divided in a plurality of drive portions and non-drive portions by grooves which reach the substrate; and a channel plate jointed to the piezoelectric device on a side where the drive layer is formed, and having a plurality of discrete ink channels formed in parts thereof respectively opposed to said plural drive portions, corresponding to nozzles for jetting ink, the non-drive portions having all regions thereof or parts of the regions where the drive electrodes are not formed.
The above-described object is also achieved by an ink jet printer head comprising: a piezoelectric device formed on a substrate, and including a drive layer having a pair of drive electrodes and a piezoelectric layer disposed between the pair of drive electrodes, the drive layer being divided in a plurality of drive portions and non-drive portions by grooves which reach the substrate; and a channel plate jointed to the piezoelectric device on a side where the drive layer is formed, and having a plurality of discrete ink channels formed in parts thereof respectively opposed to said plural drive portions, corresponding to nozzles for jetting ink, the drive electrodes have all regions thereof or parts of the region formed in a mesh.
In the above-described ink jet printer head, it is possible that the ink jet printer head further comprises: a stress removing electrode provided inside the substrate lower than the bottoms of the grooves.
In the above-described ink jet printer head, it is possible that the drive layer has a multi-layer structure having a plurality of drive electrodes and a plurality of piezoelectric layers alternately laid one on another.
The above-described object is also achieved by an ink jet printer comprising: an above-described ink jet printer head; an ink supply means for supplying ink to the discrete ink channels; and a voltage applying means for applying a voltage to the drive electrodes to displace the drive portions, whereby the drive portions are displaced by the voltage applying means to press the ink in the discrete ink channels introduced by the ink supply means so as to jet the ink through the nozzles.